They could just do what they did w. earth 90 Barry Allen (of the original Flash TV show), and show him as having aged accordingly. A 41 year old Welling as Supes isnt outrageous, if 63 year old Wesley Shipp can be the Flash.

Yeah they just have them as their post Smallville versions. People would shit themselves if they had Welling playing a seasoned Superman.

Or even better. They have Brandon Routh on Legends and Dean Cain was on Supergirl. It would be crazy if they got Welling and managed to put 4 Supermen on screen at the same time. Maybe save that for Crisis though.